Method for recovering by-products from pulp waste liquor residues



Nov. 16, 1943.

E. G. Goon'ELx. I 233455220v ASTE LIQUOR RESIDUES METHOD FOR RECOVERINGBY-PRODUCTS FRO M PULP Filed April l0, 1940 Patented Nov. 16, i943METHOD FOR BECOVERING zBY-PRODUC'IS FROM PULP WASTE LIQUOB RESIDUESEdward G. Goodeli, Stevens Point, Wis.

Application April 10, 1940, No. 328,903

' s claims. (ci. 2ozsl This invention relates to a method of recoveringb'y-'products from waste liquor residues such as those produced by thespray-drying of the waste liquors produced in the cooking of cellullosicmaterials.

In the manufacture of chemical pulp, as by the soda, sulfate or sulilteprocesses, or modifications thereof, waste cooking liquors are producedthat containY muchA of the lignin of the wood or other vegetablematerial being Pulped. as well as spent inorganic materials from theoriginal cooking liquors. It has long been known that the lignin andethaorganic residues in such waste liquors will yield valuablelay-products including methyl alcohol and acetone upon destructivedistillation. However, as Sar as I know, those skilled ess 1s designedto recoverthan' would be thesecailed black ash produced by the usualinthe speciiication and the accompanying draw-l ying'.

in the art have not been aware of the fact that Y I have now found,however-,that the spray. dried powder produced from waste cooking liquors by the processes of my Batents Nos. 1,779,535,

1,779,536, 1,779,537 and 1,779,768, all issued onl October 28, 1930, orby any other suitable drying method, is peculiarly adaptable to therecovery `view Itaken along the -line II-II of Figure 1.

Figure 3 is a flow sheet depicting the proces of the present invention.

The starting material for my process is a predrled material containinga'substantial proportion of lignin, resins and their derivatives. Suchmaterial can be obtained, as previously stated, by

spray drying waste cooking liquors such as are produced in the cookingof wood and other vegetable material by the usual chemical processes,

such as thesulfate, soda, suliite or other procof lav-products withoutthe diiliculties heretofore encountered. As the starting material forcarrying out the 'method of my present invention,

therefore, I employa pre-dried material, preferably in the form of spraydried powder, comprising the organic and inorganic solids content essesemployed in the separation of cellulose bers from the natural wood orvegetable source. While I prefer to start with a spray dried lignincontaining material, owing to the ease with which y it may be handledand its high content of substantiallyunchanged organic materials, other'methodssuchasdrumdryingoriilmdryingmay uor' having a substantial lignincontent. When obtained by the spray dryingprocs described and ciaimedinmy above enumerated patents, both the organic and inorganicconstitutents of vthe spray dried powder are present in a state richersource of the by-producis that this procbe employed in the preparationoi the starting material. Also, while the vstarting material is herereferred to as pre-dried, it may nevertheless contain an appreciable.percentage of water. say upwards of 10% or 15%, so long aait may behandled as a dry solid rather than as a liquid. Y

As best shown in Figure 1, the pre-dried start- Y ing material,preferably in the form of a loosely powdered or granulated mass, ischarged into a hopper l0 havinga lower water cooled vertical outlet Ilprovided with a valve I2 for admitting the powder into a horizontally.disposed l. retort I3 enclosed in a furnace I5. The hopper I0 is keptsuinciently full of the dry powder to actV as a seal against theentrance of air into the products desired. The

retort I3. The latter is preferably provided with a worm conveyor I4 foradvancing the powder therethrough which is driven by a motor IIa bymeans of a variable speed drive Hb allowing wide latitude in the R. P.M. of the conveyor. The furnace I5 is adapted to be heated by means of aburner I6 into which is introduced a fluid i'uel, such as oil or gas,the requisite amount of air being introduced in any suitable way toaffordl complete combustion of the fuel. The heated gaseous combustionproducts are exhausted from the oven through a stack I'I.

Electric heating elements may also be attached to the retort I3, thuseliminating the furnace I5, or the section of said retort housing theconveyor I4 may be encased in a concentric metal con` tainer throughwhich superheated steam or other` heating media are circulated.

The roof of the retort I3, except for a short section below the hopperI0, is extended vertically and closed at the top to provide a collectingchamber for the vapors which are driven oi from the powder by the heatof the furnace. As best shown in Figure 2, an outlet duct I8 leads thevapors from the retort I3 through a condenser I9 to a receiving orseparating tank 20. From the tank 20, the non-condensable portion ofsaid vapors is withdrawn through the duct 2l to a gas storage tank (notshown). The condensable portion oi said vapors is collected in the lowerportion of the receiving tank 20 and withdrawn therefrom through avalved duct 22. The tank 20 is kept partly illledvwith condensate toform a seal for the retort I3. 4

During its travel through the retort I3, the powder is substantiallycompletely charred. The vaporizable product of the distillation-passesout through the duct I8, and the remaining solid carbonaceous residue,which contains the spent cooking chemicals in dry form, is delivered bythe conveyor Il to a char box 23 (Figure 1). From the latter, the solidcarbonaceous residue vin substantially powdered form is withdrawn bymeans such as a conveyor 24, to storage (not shown). The char box 23 iskept about three quarters full to provide a seal for the retort I3.

Itwill be noted that by the* means disclosed the retort I3 is eiectivelysealed at all the three openings thereinto against the admission oi air.

The retort I3 is subjected to a higher temperature immediately below thehopper I0 than elsewhere, for the purpose of starting the 'exothermicdecomposition of the powder and for the purpose of effecting animmediate charring action which makes the powder relatively friable andnonsticky. This prompt charting of the dry powder prevents theformationof any sticky or gummy substances and thus' avoids the most troublesomefeatures heretofore encountered in the destructive distillation ofwastelliquor residues, in particular, black liquor solids.` The wormconveyor Il is driven at a speed that advances the powder through theretort I3 over an interval oi time suillcient to eiect this completecharring. Since I have found that the composition of the products of thedestructivedlstillation is aiected by the rate of advancement of thepowder, I do not flxany denite time limit for the heating of the powderin the retort I3, leaving the same to be predetermined according `,tothe nature of the temperature to which the retort I3 is heated islikewise varied in accordvancement of the powder through the retort I3.

I prefer tofeed the powder into the retort I3 at a rate which will lllthe conveyor I4 to a height roughly equal to from one-eighth to onehalfof the cross sectional area of the conveyor ilights.

. The time and intensity of the destructive distillation is obviouslyalso predetermined in accordance with the nature of the cooking liquorswhence the waste liquors are obtained.

It will readily be seen that the distilling apparatus disclosedhereinabove is distinguished by great flexibility and ease of control ofoperations carried out thereby, thus making possible the successfulcontrol of the destructive distillation of waste liquor residues, inparticular, black liquor solids, for the production of phenoliccompositions.

During the passage of the powder -through the retort I3, the powder issubjected in the absence of air to temperatures sufficiently high toeiect the destructive distillation of the organic content of thepowder.' As a result of such destructive distillation, various organiccompounds of avvolatile nature, such as methyl alcohol, acetone or itsderivatives, acetic acid, tar and others, together with water,areiormed, and the vapors of these compounds are discharged from theretort I3 through the outlet duct' I8 into the condenser I9 whence thecondensable portions of the vapors are discharged into the receivingtank 20. At the same time, the organic substances that are notdecomposed or volatilized, or the residues remaining after destructivedistillation, such as charcoal, together with the inorganic solids, aredischarged through the separate outlet for solid products formed by theopening into the char box 23.

ance with the composition desired in the 'products of the distillation.I have successfully used temperatures ranging" from 400 to 1800 F. to

The condensedportion ofthe vapors lformed during the destructivedistillation of the powder and collected in the receiving tank 20 formstwo layers, an upper aqueous layer containing methyl alcohol and acetoneand a lower tarry layer.

The latter tarry layer is separated from the aquel ous layer bydecantaton of the latter or any other suitable means.

The tar thus produced is black in color, has a speciiic gravity of 1.046and a boiling range of from to 700 F. The following is a representativeultimate analysis:

Percent dry Carbon '78.37 YHydrogen 8.31

Nitrogen 1.63 Oxygen 11.14 Sulfur y .44 Ash .11

,lowed by an extraction with sodium hydroxide or by a reversed processemploying the same steps. Various fractionsmay be isolated byiracltional distillation. Although the phenolic frac- `ltdded cost ofthe by-product tions thus isolated. have somewhat diiierentcharacteristics, they are all suitable for the preparation of protectivecoatings, varnish, and plastic resins, preservatives, and the like. Thephenolic and resinous derivatives are particularly distinguished bycompatability with wood and lignin.

The charred product may be treated to recover the spent inorganicchemicals contained therein. If the pre-dried solids are derived from asulfate black liquor, then the sodium sulfate content of thecarbonaceous residue mustfirst be reduced to sodium sulfide before theinorganic salts contained in such `carbonaceous residue can beregenerated into active cooking liquors. Accordingly, the charcoal isconveyed from the char box 23 by the conveyor 24 to a smelting furnace(not shown) where the'usual smeltlng operation iscarried out. Since thesolids delivered to the smelting furnace lare dry, or substantially so,and contain a relatively larger proportion of combustible carbonaceousmaterial, the reduction of the sulfate to sulde may be carried out inthe smeltng furnace without the use of added fuel, except in thestarting up of the smelting furnace, and without the addition of furtherquantities of carbon to eiect the desired reducing action. Sodiumsulfate, of course, may be addedto the smelting furnace in accordancewith the usual practice to make up for losses of alkali metal and sulfurin the cooking and recovery system.

Where the pre-dried solids have been derived from the soda process. thesolids from the char box 23 may be delivered into a leaching tank (notshown), into which is also introduced a sufcient quantity of weak liquoror water to effect the leaching operation. The soluble inorganic saltsare thus dissolved out of the carbonaceous residue by the weak liquor,fortifyingf the latter. From the leaching tank, the fortied weak liquorsare conducted into a dissolver or causticizing tank (not shown), wherefresh chemicals-are added as required to replace losses to prepare theliquor for normal cooking liquor composition.

The carbon remaining in the leaching tank after the soluble inorganicsalts have been leached from the carbonaceous mass delivered theretofrom the receiving tank may be utilized in a furdetails of constructionand operation may be varied through a wide range without -departing fromthe principles f this invention, and it is,

therefore, not the purpose to limit the patent theV scope of theappended claims.

I claim, as my invention: l. The method of continuously recoveringphegranted hereon otherwise than necessitated by nolic compositions fromgranular pre-dried whole` spent liquor solids obtained from spent pulpcooking liquors, which comprises forcibly conveying said solids in aloosely powdered condition into a destructive distillation zone,uickly'heat'- ing said solids during such conveyi g step to asuiiiciently high temperature primarily to char the samepand thus renderthe same relatively friable and non-sticky, then conveying the charredsolids through said destructive distillation zone while heating thecharred solids to a temperature of from 400 to 1,800 F. to distill Ythesame destructively while said solids are being conveyed through saiddestructive distillation zone, removing the vapors evolved during thedestructive distillation to a level higher than said destructivedistillation Zone so that said vapors will have a temperature of from250 to 900 F.,

conducting the vapors to a condenser, collecting the resultingcondensate, separating a tarry layer therefrom, and subjecting theseparated tar to fractional distillation and to a treatment with analkali whereby phenolic compositions may be isolated.

nace for its heat value or may be marketed as such after washing andremoval of excess moistur'e.

If the solids are obtained fromthe conventional sulfite process, thecarbonaceous residue from the receiving tank 23 can be marketed as suchor burned for its heat value.

While it is believed that'lignin furnishes the principal source fromwhich are derived the phenolic compositions obtainable by the processesaccording to this invention, the operation of my processis not tied upwith any particular theory. The important thing is that the solidscontent of waste liquors from pulping processes containing4 upwards of40 to 60 per cent of the original woodv or other vegetable material (ona dry basis) are capable of producing by the method of .destructivedistillation herein described substantial yields of phenoliccompositions adapted for the preparation of protective coatings andresins and for other purposes. This yield of phenolic compositionsrepresents a considerable saving over the recovery system and itsoperation. v

Under some conditions it has been found desirable to introduce aregulated amount of moisture, either in the form of steam or watervapor,into the retort Il. to increase the yield of by- 2. The method ofrecoveringphenolic composi- ,tions from spray dried solids obtained fromthe spray drying of spent pulp cooking liquors, which comprisesconveying said spray dried solids m a loosely powdered condition,subjecting said solids while being so conveyed to asulciently hightemperature to partially char the same and thusconvert the same directlyinto a relatively friable and non-sticky state, then conveying thecharred solids through a destructive distillation zone while heating thecharred solids to a temperature of from 400 to 1800" F. to distill thesame destructively while said solids are being conveyed through saiddestructive Adistillation zone, removing the vapors evolved during thedestructive distillation to a level higher than said destructivedistillation zone so that said vapors will have a temperature of from250 .to 900 F., conductf ing the vapors to a condenser, collecting theresulting condensate, separating a tarry layer therefrom, and subjectingthe separated tar to fractional distillation and to a treatment with analkali whereby phenolic y,compositions may be isolated. y

3. The method of recovering. phenolic compositions from spent cookingliquors in the manufacture of chemical cellulose pulp, which comprisesspray drying said spent liquors to obtain solids containing the organicand inorganic values of said spent liquors in a substantially unchangedchemical state,"-.conveying said solids in a. loosely powdered conditioninto a destructive distillation zone, subjecting said solids while beingso conveyed to a suillcientlyhigh temperature to partially char the sameand thus convert the same i I directlyinto a relatively friable andnon-sticky state, then conveying the charred solids through vsaiddestructive distillation zone while heating the charred solids to atemperature of from 400 to 1800 F. to distill the same destructivelywhilel from 250 to 900 F., conducting the vapors to a condenser,collecting the resulting condensate, separating a tarry layer therefrom,and subject- -ing the separated tar to fractional distillation and to atreatment with an alkali whereby phenolic compositions may be isolated.

EDWARD G. GOODELL.

